Kepler discovers tiny moon-sized exoplanet

Artist's conception of Kepler-37b, which is smaller than Mercury and only slightly larger than our Moon. Credit: NASA / Ames / JPL-Caltech
Artist’s conception of Kepler-37b, which is smaller than Mercury and only slightly larger than our moon. Credit: NASA / Ames / JPL-Caltech

The Kepler space telescope has added another significant discovery to its growing list – the smallest exoplanet found so far (again) orbiting a sun-like star, it was announced on Wednesday.

The new planet orbits the star Kepler-37, which is about 210 light-years away in the constellation Lyra. It is one of three planets discovered, all of which orbit their star closer than Mercury orbits our own Sun. They are therefore thought to be uninhabitable, being baked by searing heat. Kepler-37b orbits its star in only 13 days and has an estimated surface temperature of more than 426 ˚C (800 ˚F).

Despite that, the discovery is still good news for the Kepler mission, which focuses on finding smaller rocky worlds, especially ones which might be habitable and similar to Earth. As Jack Lissauer, a planetary scientist at NASA’s Ames Research Center, explains, “The fact we’ve discovered tiny Kepler-37b suggests such little planets are common, and more planetary wonders await as we continue to gather and analyze additional data.”

This smallest new planet, Kepler-37b, is smaller than Mercury and only a bit larger than our own moon. The other two planets, Kepler-37c and Kepler-37d, are slightly smaller than Venus and about twice the size of Earth, respectively.

It should be noted that the very first exoplanets found, in the early 1990s, were small worlds similar to these ones, except that they orbit a pulsar – the dead remnant of a once-living star. This made their discovery easier than finding such small planets orbiting much larger and brighter active stars like our sun.

But as Lissauer suggests, just the fact that smaller planets like our own are now thought to be common, is an exciting discovery which brings us closer to finding the first evidence for life elsewhere.

The new study has been published in the journal Nature.

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